This invention relates to improved well drilling apparatus adapted to drive a drill string without the use of a rotary table, kelly, and kelly bushing.
In order to avoid the necessity for a rotary table and its related equipment in a well drilling rig, there have been devised in the past arrangements employing a drilling unit having a pipe section connectable to the upper end of a drill string and a motor for driving that pipe section rotatively and thereby driving the string to perform a drilling operation. In some instances, the drilling unit has been mounted on a carriage which is guided by vertical tracks for movement along those tracks axially of the well to advance with the string as the drilling operation progresses. In one prior arrangement of this type, the drilling unit is connected pivotally to the carriage to swing relative to the carriage and tracks to an inclined position of alignment with a mousehole in order to pick up a pipe section from or place it into the mousehole. Abandoned Application Ser. No. 167,758 filed July 14, 1980 by Boyadjieff et al. on "Well Drilling Apparatus" shows a system in which the drilling unit is bodily shiftable horizontally between a drilling position of alignment with the well axis and a position of vertical alignment with a mousehole, and also is mounted for horizontal swinging movement relative to the main portion of the track structure to a laterally retracted position at a side of the well.